Diffusible factors such as cytokines and growth factors, and insoluble factors such as extracellular matrix (ECM) molecules are thought to be the principle mediators of crosstalk between the cellular constituents of the tumor microenvironment (Joyce et al., “Microenvironmental Regulation of Metastasis,” Nat. Rev. Cancer 9:239-52 (2009); Kenny et al., “Targeting the Tumor Microenvironment,” Front. Biosci. 12:3468-74 (2007); and Peinado et al., “The Secreted Factors Responsible for Pre-Metastatic Niche Formation Old Sayings and New Thoughts,” Semin. Cancer Biol. 21(2):139-146 (2011)). However, accumulating evidence suggests that the release of membrane vesicles also mediate communication between cells on both a local and systemic level (Peinado et al., “The Secreted Factors Responsible for Pre-Metastatic Niche Formation: Old Sayings and New Thoughts,” Semin. Cancer Biol. 21(2):139-146 (2011); Iero et al. “Tumour-Released Exosomes and their Implications in Cancer Immunity,” Cell Death Differ. 15:80-8 (2008); Ratajczak et al., “Membrane-Derived Microvesicles: Important and Underappreciated Mediators of Cell-To-Cell Communication,” Leukemia 20:1487-95 (2006); Muralidharan-Chari et al., “Microvesicles: Mediators of Extracellular Communication During Cancer Progression,” J. Cell Sci. 123:1603-11 (2010); Cocucci et al., “Shedding Microvesicles: Artefacts no More,” Trends Cell Biol. 19:43-51 (2009); and van Niel et al., “Exosomes: A Common Pathway for a Specialized Function,” J. Biochem. 140:13-21 (2006)).
Although, microvesicles and exosomes were initially thought to be products of a pathway used to release excess material from cells; they have been shown to mediate morphogen signaling, immunological signaling, cell recruitment, and horizontal transfer of genetic material (Ratajczak et al., “Membrane-Derived Microvesicles: Important and Underappreciated Mediators of Cell-To-Cell Communication,” Leukemia 20:1487-95 (2006) and Valadi et al., “Exosome-Mediated Transfer of mRNAs and MicroRNAs is a Novel Mechanism of Genetic Exchange Between Cells,” Nat. Cell Biol. 9:654-9 (2007)). Exosomes are small vesicles (30-100 nm) derived from the luminal membranes of late endosomes/multivesicular bodies (MVB), and are constitutively released via the fusion of MVBs with the cell membrane (Thery et al., “Exosomes: Composition, Biogenesis and Function,” Nat. Rev. Immunol. 2:569-79 (2002) and Fevrier et al., “Exosomes: Endosomal-Derived Vesicles Shipping Extracellular Messages,” Curr. Opin. Cell Biol. 16:415-21 (2004)). Exosomes secreted by tumor cells have been recently implicated in all stages of tumor progression (Peinado et al., “The Secreted Factors Responsible for Pre-Metastatic Niche Formation: Old Sayings and New Thoughts,” Semin. Cancer Biol. 21(2):139-146 (2011); Iero et al. “Tumour-Released Exosomes and their Implications in Cancer Immunity,” Cell Death Differ. 15:80-8 (2008); and van Niel et al., “Exosomes: A Common Pathway for a Specialized Function,” J. Biochem. 140:13-21 (2006)). Studies have found that tumor exosomes are involved in the cell-cell communication, such as the horizontal transfer of information (i.e. mRNAs, microRNAs and proteins) between stem cells (Ratajczak et al., “Embryonic Stem Cell-Derived Microvesicles Reprogram Hematopoietic Progenitors: Evidence for Horizontal Transfer of mRNA and Protein Delivery,” Leukemia 20:847-56 (2006) and Janowska-Wieczorek et al., “Platelet-Derived Microparticles Bind to Hematopoietic Stem/Progenitor Cells and Enhance their Engraftment,” Blood 98:143-9 (2001)), endothelial cells (Al-Nedawi et al., “Endothelial Expression of Autocrine VEGF upon the Uptake of Tumor-Derived Microvesicles Containing Oncogenic EGFR,” Proc. Natl. Acad. Sci. U.S.A. 106:3794-9 (2009) and Nazarenko et al., “Cell Surface Tetraspanin Tspan8 Contributes to Molecular Pathways of Exosome-Induced Endothelial Cell Activation,” Cancer Res. 70:1668-78 (2010)), fibroblasts (Webber et al., “Cancer Exosomes Trigger Fibroblast to Myofibroblast Differentiation,” Cancer Res. 70:9621-30 (2010)), bone marrow-derived cells (BMDCs) (Valadi et al., “Exosome-Mediated Transfer of mRNAs and MicroRNAs is a Novel Mechanism of Genetic Exchange Between Cells,” Nat. Cell Biol. 9:654-9 (2007); Ratajczak et al., “Embryonic Stem Cell-Derived Microvesicles Reprogram Hematopoietic Progenitors Evidence for Horizontal Transfer of mRNA and Protein Delivery,” Leukemia 20:847-56 (2006); Baj-Krzyworzeka et al., “Tumour-Derived Microvesicles Carry Several Surface Determinants and mRNA of Tumour Cells and Transfer some of these Determinants to Monocytes,” Cancer Immunol. Immunother. 55:808-18 (2006); Liu et al., “Contribution of MyD88 to the Tumor Exosome-Mediated Induction of Myeloid Derived Suppressor Cells,” Am. J. Pathol. 176:2490-9 (2010); Xiang et al., “Induction of Myeloid-Derived Suppressor Cells by Tumor Exosomes,” Int. J. Cancer 124:2621-33 (2009); and Yu et al., “Tumor Exosomes Inhibit Differentiation of Bone Marrow Dendritic Cells,” J. Immunol. 178:6867-75 (2007)), and tumor cells (Al-Nedawi et al., “Intercellular Transfer of the Oncogenic Receptor EGFRvIII by Microvesicles Derived from Tumour Cells,” Nat. Cell Biol. 10:619-24 (2008); and Hao et al., “Epigenetic Transfer of Metastatic Activity by Uptake of Highly Metastatic B16 Melanoma Cell-Released Exosomes,” Exp. Oncol. 28:126-31 (2006); and Skog et al., “Glioblastoma Microvesicles Transport RNA and Proteins that Promote Tumour Growth and Provide Diagnostic Biomarkers,” Nat. Cell Biol. 10:1470-6 (2008)).
It is now well recognized that BMDCs play a crucial role in the generation of a suitable microenvironment for the primary tumor and the development of metastasis through a process called “pre-metastatic niche formation” (Joyce et al., “Microenvironmental Regulation of Metastasis,” Nat. Rev. Cancer 9:239-52 (2009); Wels et al., “Migratory Neighbors and Distant Invaders: Tumor-Associated Niche Cells,” Genes Dev. 22:559-74 (2008); Psaila et al., “The Metastatic Niche: Adapting the Foreign Soil,” Nat. Rev. Cancer 9:285-93 (2009); Kaplan et al., “VEGFR1-Positive Haematopoietic Bone Marrow Progenitors Initiate the Pre-Metastatic Niche,” Nat. 438:820-7 (2005); Guise, T., “Examining the Metastatic Niche: Targeting the Microenvironment,” Semin. Oncol. 37 Suppl. 2:S2-14 (2010); and Gao et al., “Bone Marrow-Derived Endothelial Progenitor Cells Contribute to the Angiogenic Switch in Tumor Growth and Metastatic Progression,” Biochim. Biophys. Acta. 1796:33-40 (2009)). Although secreted factors such as vascular endothelial growth factor-A (VEGF-A), placental growth factor (P/GF), transforming growth factor-beta (TGF-β), tumor necrosis alpha (TNF-α), and lysyl oxidase (LOX) are known contributors to BMDCs recruitment to both primary tumor and pre-metastatic niches (Kaplan et al., “VEGFR1-Positive Haematopoietic Bone Marrow Progenitors Initiate the Pre-Metastatic Niche,” Nat. 438:820-7 (2005); Erler et al., “Hypoxia-Induced Lysyl Oxidase is a Critical Mediator of Bone Marrow Cell Recruitment to Form the Premetastatic Niche,” Cancer Cell. 15:35-44 (2009); and Hiratsuka et al., “Tumour-Mediated Upregulation of Chemoattractants and Recruitment of Myeloid Cells Predetermines Lung Metastasis,” Nat. Cell. Biol. 8:1369-75 (2006)), the potential contribution of exosomes to this process has yet to be evaluated.
The present invention is directed to overcoming these and other deficiencies in the art.